Linear actuator using magnetostrictive power element

ABSTRACT

A linear actuator includes a substantially cylindrical magnetostrictive element disposed in a housing. A retainer is cooperatively engaged with the housing and an exterior of the magnetostrictive element such that relaxed portions of the magnetostrictive element are frictionally retained in the retainer. An actuator rod is functionally coupled to one longitudinal end of the magnetostrictive element. A biasing device is disposed between the housing and the retainer to maintain the retainer in lateral compression. The actuator includes magnets arranged to induce peristaltic motion in the magnetostrictive element.

CROSS-REFERENCE TO RELATED APPLICATIONS

Priority is claimed from U.S. Provisional Application No. 60,865,884filed on Nov. 15, 2006 and entitled “Cylindrical Actuator UsingMagnetostrictive Element.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of linear actuators. Morespecifically, the invention relates to linear actuators usingmagnetostrictive elements to generate linear motion.

2. Background Art

Linear actuators have wide application in devices used in connectionwith wellbores drilled through the Earth's subsurface. For example, suchactuators are known in the art be used to operate subsurface safetyvalves or other valves. Such actuators are also known in the art to beused to open and close back up arms or pads on well logging devices, orto actuate steering devices in certain drilling tools such as rotarysteerable directional drilling systems.

Irrespective of the particular use, linear actuators used in connectionwith wellbore devices are most commonly of two types. One type includesa motor that drives a screw or worm gear. The screw or worm gear iscoupled to a ball nut. Rotation of the screw is translated into linearmotion of the ball nut. See, e.g., U.S. Pat. No. 6,898,994 issued toWalton.

The other type of actuator in widespread use is hydraulic. Typically, amotor drives an hydraulic pump, and pressure from the pump (which may bestored in an accumulator or similar reservoir) is selectively applied toone side or the other of a piston disposed in a cylinder. The force ofthe pressurized hydraulic fluid acting on the piston moves the pistonalong the cylinder. See, e.g., U.S. Pat. No. 5,673,763 issued to Thorpand presently owned by the assignee of the present invention.

Electric linear actuators are known in the art. See, e.g., U.S. Pat. No.6,100,609 issued to Weber. Many electric linear actuators operate on aprinciple similar to the motor/ball screw combination referred to above.Typically such combination of motor and reduction gear is necessary forthe actuator to produce the force required to operate the wellboredevice. Electric linear motors known in the art are typically unable toproduce such force absent a reduction gear.

More recently, magnetostrictive elements have been used to produce alinear actuator. See, for example, Won-Jong Kim et al., Extended-RangeLinear Magnetostrictive Motor with Double-Sided Three-Phase Stator”,IEEE Transactions on Industry Applications vol. 38, no. 3 (May/June2002). The actuator described in the foregoing publication uses, for apower producing element, a magnetostrictive material such as one soldunder the trademark ETREMA TERFENOL-D, which is a registered trademarkof Edge Technologies, Inc., Ames, Iowa. The magnetostrictive element isin the form of a rectangular slab placed between two tight-fittingarmatures. The armatures are subjected to a magnetic field generated bymultiphase alternating current, such that the magnetic field “moves” ina manner similar to that of an electric induction motor. The magneticfield alternatingly causes magnetostriction of part of themagnetostrictive element and its consequent elongation normal to themagnetostriction, while other parts of the magnetostrictive elementremain tightly held within the armatures. The friction between thestationary armatures and the uncompressed part of the magnetostrictiveelement provides the reaction force required to move the elongating partof magnetostrictive element against a load, causing the load to move. By“moving” the magnetic field along the armatures, the magnetostrictiveelement undergoes peristaltic or “inchworm” like motion, thus moving theload.

The foregoing linear actuator has been difficult to adapt to wellboredevices because of its shape.

Another type of linear actuator using a magnetostrictive materialelement is disclosed in Bryon D. J. Snodgrass, Precision moves withmagnetostriction, MachineDesign.com (Nov. 18, 2004). The foregoingactuator does not have any mechanism to compensate for thermal expansionor wear of moving elements.

There continues to be a need to improved linear actuators for use inconnection with wellbore devices.

SUMMARY OF THE INVENTION

One aspect of the invention is a linear actuator. A linear actuatoraccording to this aspect of the invention includes a substantiallycylindrical magnetostrictive element disposed in a housing. A retaineris cooperatively engaged with the housing and an exterior of themagnetostrictive element such that relaxed portions of themagnetostrictive element are frictionally retained in the retainer. Anactuator rod is functionally coupled to one longitudinal end of themagnetostrictive element. A biasing device is disposed between thehousing and the retainer to maintain the retainer in lateralcompression. The actuator includes magnets arranged to induceperistaltic motion in the magnetostrictive element.

A method for operating a wellbore device according to another aspect ofthe invention includes applying inwardly radial biasing force to aretainer surrounding a substantially cylindrical magnetostrictiveelement to maintain frictional contact between the retainer and relaxedportions of the magnetostrictive element. A magnetic field is applied tothe magnetostrictive element to cause peristaltic motion in themagnetostrictive element. The peristaltic motion at a longitudinal endof the magnetostrictive element is then transferred to an operatingelement of the wellbore device.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut away view of one example linear actuator according tothe invention.

FIG. 2 is a cross section through the example actuator shown in FIG. 1.

FIG. 3 shows one example of an electric power supply used to operate theactuator of FIG. 1.

FIG. 4 shows an example of a wireline conveyed formation fluid testinginstrument using an actuator according to the invention.

FIG. 5 shows an example of a wireline conveyed formation densitymeasuring instrument using an actuator according to the invention.

FIG. 6 shows an example of a completion valve using an actuatoraccording to the invention.

FIG. 7 shows an example of a rotary steerable directional drillinginstrument that can use actuators according to the invention as asteering device.

DETAILED DESCRIPTION

One example of a linear actuator according to the invention is shown incut away view in FIG. 1. The actuator 10 may be disposed inside agenerally cylindrical housing 16 such as may be made from a highstrength, preferably non-magnetic metal or metal alloy such as monel,titanium or an alloy sold under the trademark INCONEL, which is aregistered trademark of Huntington Alloys Corp., Huntington, W. Va. Thehousing 16 can include a tapered interior bore 18 that cooperativelyengages the outer surface of correspondingly tapered wedges 14 disposedaround the exterior of a magnetostrictive element retainer 12. Thewedges 14 will be further explained below. The housing 16 is generallyopen at its longitudinal ends to enable insertion and operation of thevarious internal components of the actuator 10. A plurality of magnetsmay be disposed on an exterior surface of the housing 16. The magnetsmay be wire coils 40 wound so as to produce, when electricallyenergized, a generally longitudinally polarized, moving magnetic fieldinside the housing 16. The source of electric power used to energize thecoils 40 will be further explained with reference to FIG. 3.

The magnetostrictive element retainer 12 (for convenience hereinafter“retainer”) may also be made from high strength, non-magnetic materialsuch as monel, titanium, or the INCONEL-brand alloy referred to above,and is disposed generally inside the housing 16 as shown in FIG. 1. Asexplained above, the retainer 12 may include a plurality ofcircumferentially spaced apart, tapered wedges 14 extending laterallyoutward on at least a portion of the exterior surface of the retainer12. When the retainer 12 is longitudinally urged into the housing 16,the wedges 14 are laterally urged inwardly by cooperatively engaging thetapered interior bore 18. Longitudinal force may be provided to theretainer 12 by a spring 24 or similar biasing device cooperativelyengaged between a flange 20 at one longitudinal end of the retainer 12and a retainer nut 22 that may be threadedly engaged (see 26 in FIG. 1)with an inside surface of one longitudinal end of the housing 16. Forceexerted by the spring 24 against the flange 20 urges the retainer 12longitudinally into the housing 16 so that the tapered bore 18 exertslateral compressive force against the wedges 14. The retainer 12 mayinclude longitudinally extending slots (see 14A in FIG. 2) between theinterior surfaces of the wedges 14 to enable lateral compression of thewedges 14 to be more freely transferred to the interior of the retainer12.

A magnetostrictive element 28 may be disposed inside the retainer 12 asshown in FIG. 1. The magnetostrictive element 28 may be generally in theshape of an annular cylinder, enabling passage therethrough of anactuator rod or tube 34. The magnetostrictive element 28 may be madefrom a material known in the art as Terfenol-D and sold under thetrademark ETREMA TERFENOL-D referred to in the Background sectionherein. Terfenol-D is preferred as a material for the magnetostrictiveelement 28 because of its very high degree of magnetostriction withrespect to the magnitude of applied magnetic field, and the amount offorce generated by its magnetostriction. The Terfenol-D material alsohas a curie temperature of about 380 degrees C. and is thus relativelyinsensitive to temperatures existing in typical wellbores. However, theexact composition of the magnetostrictive element 28 is not a limit onthe scope of the present invention.

The magnetostrictive element 28 has an external diameter in its relaxedstate (not subjected to a magnetic field) selected to provide a tightfriction fit within the interior of the retainer 12. One longitudinalend of the magnetostrictive element 28 is cooperatively engaged with aretainer nut 30 that is threadedly engaged on a portion of the actuatorrod or tube 34. The other longitudinal end of the magnetostrictiveelement 28 is in contact with one side of a thrust washer 33 that on itsother side is in contact with one end of a coil spring 32 or similarbiasing device. The spring 32 is in contact at its other end with athrust face 36 on the exterior of the actuator rod or tube 34. Thecombination of retainer nut 30, spring 32 and thrust face 36 maintainsthe magnetostrictive element 28 in compression as it moves along theinterior of the retainer 12 to longitudinally drive the actuator rod ortube 34. The actuator rod or tube 34 may be constrained to movelongitudinally inside the housing 16 by journal bearings 38 or similarlinear bearings disposed inside the housing 16 and external to thesurface of the actuator rod or tube 34.

In operation of the actuator 10, electric current selectively passedthrough the coils 40 causes a portion of the magnetostrictive element 28to laterally compress (under magnetostriction) enough so as to be ableto move longitudinally within the retainer 12, and this same portionundergoes longitudinal elongation. The relaxed portions of themagnetostrictive element 28 remain frictionally fixed within the innersurface of the retainer 12. As the current through the coils 40 isselectively changed, the portions of the magnetostrictive element 28that are laterally compressed and longitudinally elongated can beselectively changed, such that the entire magnetostrictive element 28longitudinally translates with respect to the retainer 12 in aperistaltic or “inch worm” type motion. Because the magnetostrictiveelement 28 is ultimately longitudinally fixed between the retainer nut30 and the thrust face 36, longitudinal translation of themagnetostrictive element 28 will cause corresponding longitudinaltranslation of the actuator rod or tube 34. Although not shown in FIG.1, any device intended to be operated by a linear actuator may befunctionally coupled to one end of the actuator tube 34.

The foregoing example includes what is described as an actuator rod ortube 34. If in the form of a tube, and as will be explained withreference to FIG. 6, the actuator rod or tube 34 may include a generallyopen through passage or bore 34A. In such implementations, the actuator10 may be used, for example, to operate a wellbore valve, such as asubsurface safety valve, wherein a production tubing or similar conduitmay pass through the actuator 10. In such implementations, the actuator10 may be disposed in an annular space between the wellbore (which maybe cased) and an exterior of a production tubing, See, e.g., U.S. Pat.No. 6,513,594 issued to McCalvin et al. and assigned to the assignee ofthe present invention for an example of one type of valve. Another typeof wellbore valve will be explained below with reference to FIG. 6. Itshould be clearly understood that the application of the presentinvention is not limited to use with wellbore valves, nor must theactuated element of the actuator be in the form of a tube as in FIG. 1.Other examples may use a solid rod or similar device that may belongitudinally moved by the magnetostrictive element 28 while clearlyremaining within the scope of the present invention.

A cross section of the actuator is shown in FIG. 2 to illustrate thecooperative arrangement of the wedges 14 with the tapered interior bore18. A particular advantage that may be provided by the cooperativearrangement of the blades and tapered interior bore 18 is that as theretainer 12 and/or the magnetostrictive element 28 are subject to wear,thermal expansion in a wellbore and/or machining tolerances, asufficient amount of friction can be maintained between themagnetostrictive element 28 and the retainer 12 to enable the abovedescribed translational motion of the magnetostrictive element 28 whileexerting force against a load coupled to the actuator tube (34 in FIG.1).

One example of energizing the coils 40 is shown in FIG. 3. A multiphasealternating current source 42, which may be a three phase source, can becoupled as shown to the coils 40 such that a longitudinally “traveling”magnetic field may be exerted on the magnetostrictive element (28 inFIG. 1). As another example, the coils may have a three phase armaturecommutation. Each phase is made of several coils connected in series toform a number a poles. The pole pitch is preferably one half of thelength of the magnetostrictive element (28 in FIG. 1). In either of theforegoing examples, the speed of motion of the actuator tube (34 inFIG. 1) may be controlled by selecting the alternating currentfrequency.

One example of a formation fluid testing instrument 44 that may beconveyed into a wellbore 41 at the end of an armored electrical cable 43is shown in FIG. 4. The fluid testing instrument 44 may be of a typethat engages a probe sealed by a packing element (collectively shown at45) against a wall of the wellbore 41. The probe is thus sealinglyengaged with the formation. In such instruments, it is known in the artto urge the instrument housing to one side of the wellbore to facilitatesealing engagement of the packing element with the formation. In theexample shown in FIG. 4, two lines actuators 10 as explained withreference to FIGS. 1-3 may be included in the instrument 44 and arrangedto extend transversely to the longitudinal axis of the instrument 44.When extended, the actuator tubes 34 engage the wall of the wellbore tourge the instrument 44 into contact with the opposite side of thewellbore 41. In such implementations, the actuator tubes 34 may includeshoes or pads 34A disposed at the contacting ends thereof to limitindentation of the wellbore wall by the actuator tubes 34. One exampleof a formation testing instrument is described in U.S. Pat. No.3,952,588 issued to Whitten and assigned to the assignee of the presentinvention.

An example of a formation density measuring instrument 46 is shown inFIG. 5. The density instrument 46 typically includes a “skid” 48 havinga gamma radiation source and gamma radiation detectors (not shownseparately therein) for engagement with the wall of the wellbore. Anactuator 10 as explained above may have its actuator tube 34 coupled toa pivotally extending back up arm 50. Typically the actuator 10 will bearranged along the longitudinal axis of the instrument 46 such thatextension of the actuator tube 34 therefrom will laterally extend theback up arm 50. See, e.g., U.S. Pat. No. 5,528,029 issued to Chappelatet al. and assigned to the assignee of the present invention for adescription of a suitable back up arm linkage that may use an actuatoraccording to the invention.

FIG. 6 shows an example of a completion valve that may be used with anactuator according to the invention. A wellbore may have a casing 60 orsimilar pipe cemented therein. In a selected formation, the casing 60may include perforations 58 to provide hydraulic communication to theinterior of the casing 60 from the formation outside thereof. Aproduction tubing 54 may extend through the interior of the casing 60and may define a sealed annular space therein between one or moreannular sealing devices (“packers”) 55. The tubing 54 may itself includeperforations 56 in between the packers 55 such that exposure of thetubing perforations 56 may enable fluid to enter the casing 60 and thetubing 54. The tubing perforations 56 may be selectively exposed orclosed using a sliding sleeve valve 52. In the present example, anactuator 10 may be operatively coupled to the sliding sleeve valve 52,such that extension of the actuator tube 34 may move the sleeve valve 52to cover the tubing perforations 56 thus stopping fluid entry from thecasing 60 through the tubing perforations 56. Retraction of the actuatortube 34 will open the sliding sleeve valve 52.

An example of a rotary steerable directional drilling instrument thatcan use actuators according to the invention is shown in FIG. 7. Theinstrument 71 in the present example is a so-called “push the bit”instrument, but the application of an actuator according to theinvention is not limited to push the bit instruments. The instrument 71includes a drive shaft 72 that includes an upper threaded connection 78configured to threadedly coupled to a drill string (not shown). Thedrive shaft 72 is rotated along with the drill string (not shown) torotate a drill bit 76 disposed at the lower end of the instrument 71.Typically, the drive shaft 72 will include a female threaded connection(“box end”) to threadedly couple to the drill bit 76 or a near-bitdrilling tool (not shown). The drive shaft 72 is disposed in a housing70 that is rotatably disposed about the exterior of the drive shaft 72.The housing includes a plurality of actuators 10 disposed atcircumferentially spaced apart positions about the housing 70 andarranged such that the respective actuator rods 34 extend laterallyoutwardly from the center of the housing 70. Each actuator rod 34 may becovered by a pad 34B to protect the rod 34 from damage. Each actuator 10is coupled to a directional sensing and actuator control circuit system80. The system 80 includes sensors (not shown separately) that determinethe geodetic orientation of the housing 70 and selectively extend onesof the actuators 10 to cause the instrument 71 to exert lateral force.The lateral force is selected to cause the longitudinal axis of theinstrument to be oriented along a selected trajectory (and thus “steer”a wellbore along such trajectory. Rotary steerable directional drillinginstruments known in the art prior to the present invention typicallyuse hydraulic actuators to perform the same or similar function as theactuators 10 in the example instrument above.

The foregoing examples of wellbore devices are not intended to be anexhaustive list, but only a limited representation of the types ofwellbore devices that may be used with actuators made according to theinvention.

A linear actuator made according to the invention may have manyapplications in wellbore instruments and controls. Such actuators cangenerate substantial operating forces with relatively small activeelements, can be configured to operate in many different geometries andeliminate a large number of moving parts associated with motor/ball nutand hydraulic linear actuators.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A method for operating a wellbore device, comprising: applyinginwardly radial biasing force to a retainer surrounding a substantiallycylindrical magnetostrictive element to maintain frictional contactbetween the retainer and relaxed portions of the magnetostrictiveelement, wherein the applying inwardly radial biasing force compriseslongitudinally biasing the retainer in a housing, the retainer andhousing having cooperative surfaces arranged to radially compress theretainer in response to longitudinal biasing thereof in the housing;applying a magnetic field to the magnetostrictive element to causeperistaltic motion in the magnetostrictive element; and transferring theperistaltic motion at a longitudinal end of the magnetostrictive elementto an operating element of the wellbore device.
 2. The method of claim 1wherein the applying a magnetic field comprises applying electriccurrent to a plurality of wire coils wound longitudinally outside theretainer.
 3. The method of claim 1 wherein the operating elementcomprises a back up pad on a formation testing instrument.
 4. The methodof claim 1 wherein the operating element comprises a back up arm on adensity measuring instrument.
 5. The method of claim 1 wherein theoperating element comprises a steering element on a rotary steerabledirectional drilling instrument.
 6. The method of claim 1 wherein theoperating element comprises a wellbore sleeve valve.
 7. The method ofclaim 1 further comprising passing a wellbore tubular longitudinallythrough the magnetostrictive element.
 8. A method for operating awellbore device, comprising: applying inwardly radial biasing force to aretainer surrounding a substantially cylindrical magnetostrictiveelement to maintain frictional contact between the retainer and relaxedportions of the magnetostrictive element; applying a magnetic field tothe magnetostrictive element to cause peristaltic motion in themagnetostrictive element by applying electric current comprisingmultiphase alternating current to a plurality of wire coils woundlongitudinally outside the retainer; and transferring the peristalticmotion at a longitudinal end of the magnetostrictive element to anoperating element of the wellbore device.
 9. The method of claim 8wherein the operating element comprises a back up pad on a formationtesting instrument.
 10. The method of claim 8 wherein the operatingelement comprises a back up arm on a density measuring instrument. 11.The method of claim 8 wherein the operating element comprises a steeringelement on a rotary steerable directional drilling instrument.
 12. Themethod of claim 8 wherein the operating element comprises a wellboresleeve valve.
 13. The method of claim 8 further comprising passing awellbore tubular longitudinally through the magnetostrictive element.